I’m planning to translate it, but since I don’t actually know the island language, I’ll be basing it on Kojima’s explanation in episode… 8, I think, supplemented by whatever similarities the island language has with Japanese.

I have the same problem! I love Teidanuhikyari. According to Wikipedia, the island language itself is an endangered language. :( But the person who sang it, Nami Miyahara, knows English and Japanese. Maybe we could ask her what the lyrics are!